Used in the same way as the set prefixes used by Bethesda.
Date
Meant to help show if the book is a current publication or comes from a previous era.
Merethic Era - High Elven wizard towers at Ald Redaynia, Bal Fell, Tel Aruhn, and Tel Mora are built. Dwemer Freeholds are constructed. High Velothi Culture thrives in Resdayn (may coincide with the construction of Strongholds and the propylon system). High Velothi Culture fails and splits into the Ashlander tribes and Great Houses.
First Era - Morrowind/Resdayn conquered by the First Empire of the Nords. The Nords are driven out of Morrowind. War of the First Council; Vvardenfell erupts. Dwemer disappear. Worship of the Tribunal begins. Second Empire declares war on Morrowind.
Second Era - Second Akaviri Invasion affects parts of Morrowind. Dagoth Ur reawakens. Tiber Septim conquers Tamriel; Armistice is signed.
Rarity
Popular - can commonly be found all over, including households (shows up in random loot).
Niche - only owned by individuals or institutions with a particular interest in the subject (shows up rarely in random loot).
Rare - only found in specific locations (does not show up in random loot).
Source
OOG - From an Out Of Game developer text.
original - Original text written by The Elder Scrolls community members.
A technical manual containing reference data calculated by the Guild of Astrologers for the convenience of mariners, surveyors, mages, scholars, and travelers of all kinds.
